The present invention relates generally to the formation of dielectric films. More specifically, the invention relates to dielectric materials and films comprising same having a low dielectric constant and enhanced mechanical properties and methods for making same.
All references, including publications, patent applications, and patents, cited herein are hereby incorporated by reference to the same extent as if each reference were individually and specifically indicated to be incorporated by reference and were set forth in its entirety herein.
There is a continuing desire in the microelectronics industry to increase the circuit density in multilevel integrated circuit devices such as memory and logic chips to improve the operating speed and reduce power consumption. In order to continue to reduce the size of devices on integrated circuits, the requirements for preventing capacitive crosstalk between the different levels of metallization becomes increasingly important. These requirements can be summarized by the expression “RC”, whereby “R” is the resistance of the conductive line and “C” is the capacitance of the insulating dielectric interlayer. Capacitance “C” is inversely proportional to line spacing and proportional to the dielectric constant (k) of the interlayer dielectric (ILD). Such low dielectric materials are desirable for use, for example, as premetal dielectric layers or interlevel dielectric layers.
A number of processes have been used for preparing low dielectric constant films. Chemical vapor deposition (CVD) and spin-on dielectric (SOD) processes are typically used to prepare thin films of insulating layers. Other hybrid processes are also known such as CVD of liquid polymer precursors and transport polymerization CVD. A wide variety of low k materials deposited by these techniques have been generally classified in categories such as purely inorganic materials, ceramic materials, silica-based materials, purely organic materials, or inorganic-organic hybrids. Likewise, a variety of processes have been used for curing these materials to, for example, decompose and/or remove volatile components and substantially crosslink the films, such as heating, treating the materials with plasmas, electron beams, or UV radiation.
The industry has attempted to produce silica-based materials with lower dielectric constants by incorporating organics or other materials within the silicate lattice. Undoped silica glass (SiO2), referred to herein as “USG,” exhibits a dielectric constant of approximately 4.0. However, the dielectric constant of silica glass can be lowered to a value ranging from 2.7 to 3.5 by incorporating terminal groups such as fluorine or methyl into the silicate lattice. These materials are typically deposited as dense films and integrated within the IC device using process steps similar to those for forming USG films.
It is known that silicon dioxide (SiO2) films have a hardness of ˜7 GPa but also have a dielectric constant (k) of 3.8-4.2. The dielectric constant (k) of a material generally cannot be reduced without a subsequent reduction in the mechanical properties, i.e., elastic modulus (Young's modulus), hardness, toughness, of the material. Mechanical strength is needed for subsequent processing steps such as etching, CMP (“Chemical Mechanical Planarization”), and depositing additional layers such as diffusion barriers for copper, copper metal (“Cu”), and cap layers on the product. Mechanical integrity, or stiffness, compressive, and shear strengths, may be particularly important to survive CMP. It has been found that the ability to survive CMP may be correlated with the elastic modulus of the material, along with other factors including polishing parameters such as the down force and platen speed. See, for example, Wang et al., “Advanced processing: CMP of CU/low-.kappa. and Cu/ultralow-k layers,” Solid State Technology, September, 2001; Lin et al., “Low-k Dielectrics Characterization for Damascene Integration,” International Interconnect Technology Conference, Burlingame, Calif., June, 2001. These mechanical properties are also important in the packaging of the final product. Because of the trade-off in mechanical properties, it may be impractical to use certain porous low dielectric compositions.
There are known ways to improve the mechanical properties of as-deposited silicate films. For Example, U.S. Pat. No. 7,932,188 discloses a UV annealing step performed on a porous OSG wherein the film after exposure exihits an at least 10% improvement in its hardness and elastic modulus. Although it is known that OSG films can be deposited with dielectric constans in the range of 2.8 to 3.1, it has not been possible to deposit these films with hardnesses approaching 4.0 GPa, even after UV annealing. Accordingly, there is a need in the art for a class of OSG precursor compounds to form a dense OSG film that has a dielectric constant of 2.8 to 3.1 and which has an increased Hardness as measured in gigapascals (GPa).